1. Field of the Invention
The present invention relates to door opening sensing and alarm producing devices which provide an audio alarm when the opening of a door is sensed.
2. Description of the Prior Art
Heretofore various types of devices have been proposed for detecting the presence of an intruder or more specifically the act of entry by an intruder into a protected area such as by the opening of a door.
Many of these devices have consisted in means for sensing when a door has been opened by an unauthorized person. Examples of such previously proposed intruder detection alarm devices and related devices are disclosed in the following patents.
______________________________________ U.S. PAT. NO. PATENTEE ______________________________________ 3,846,782 Brodsky 3,866,201 Beiswenger 3,938,120 O'Connell 3,986,183 Fujiwara 4,057,773 Cohen 4,059,832 Conklin ______________________________________
The use of movement of a magnet in a door alarm system is disclosed in the Fujiwara U.S. Pat. No. 3,986,183 and the Cohen U.S. Pat. No. 4,057,773 referred to above.
Also it is known from the O'Connell U.S. Pat. No. 3,938,120 to provide a mechanism which will produce a desired sound, namely a voice message, when a door is opened.
Also, a security alarm device for providing a variable pitch siren sound utilizing a free-running multivibrator and a relaxation type saw tooth oscillator is disclosed in the Beiswenger U.S. Pat. No. 3,866,201.
Still further, there is disclosed in the Brodsky U.S. Pat. No. 3,846,782 an intruder detection system for protecting an area with a keyboard inhibitor for re-entry which is utilized for controlling a detection and surveillance system having an alarm. In this patent, there is disclosed an alarm system with multiple modes and a reset keyboard. However the reset keyboard is mounted for actuation from outside the area being protected. Also the detection system disclosed in this patent utilizes silicon controlled rectifiers and three transistors which prevent one from depressing three switches simultaneously. This circuit arrangement is not unlike a train signal "interlock" that allows only one of three levers to be moved at a time. Also in addition to connecting the three switches, the remaining switches utilized must be strapped to a reset transistor.
As will be described in greater detail hereinafter, the device of the present invention differs from the previously proposed intruder alarm detection devices and systems by providing a simple system utilizing a relatively simple circuit which requires that the keys must be struck in a proper timed (slow) sequence and must correspond to a predetermined number stored in the circuit to stop or inhibit operation of an audio alarm.
More specifically, the storing of the number is achieved by three programming leads and by providing circuit connections such that striking the wrong key still clears the memory without connecting other leads.
Moreover, the intruder alarm device of the present invention differs from the previously proposed devices by providing reed switches or relays and by providing an alarm circuit, a doorbell circuit and a visitor announcing circuit in the same device.